Field of the Invention
The invention relates to a method for detecting the position of a switching device in an encapsulated switching installation, as well as a switching installation having a device for that purpose.
High or medium voltage switching installations generally require that there be a position indicator for the switching devices being used. That represents a problem in metal-encapsulated switching installations, since the switch position cannot be seen from the outside. In order to detect a position, mechanical devices have to be passed out of the encapsulation, for example, or cable-based detection devices having sensors, in particular contacts, have to be used.
Such devices are very costly and in each case are aimed only at the information specifically to be detected. In addition, the position information frequently also has to be electrically converted and processed, which results in a cost for wiring and signal processing.
German Utility Model 94 20 199 discloses a metal-encapsulated high-voltage switching installation in which a surface acoustic wave element (SAW) is disposed in one of its gas areas. The SAW is used to verify gas constituents, which are produced by the effect of arcing on the extinguishing gas that is contained in the encapsulation, or for detection of pressure waves. In that case, an antenna, which is used for wireless information transmission to an evaluation device, is disposed on the outside of the encapsulation.
The use of SAW sensors in high-voltage technology is disclosed in principle in an article entitled "Akustische Oberflachenwellen-Technologie fur Innovationen" (Surface Acoustic Wave Technology for Innovations) from Siemens-Zeitschrift Spezial [Siemens Journal, Special) FuE, Spring 1994. It has also already been provided in that case for the SAW sensor to be mounted in the container and for its antenna to be mounted externally.
In principle, the state of the art discloses the detection of the position of a switching device through the use of the so-called "light barrier technique". A measuring light beam is likewise interrupted by a movable part of the switching device, and a message signal is derived therefrom. Reference is made in that regard to U.S. Pat. No. 4,945,256.
In Published French Patent Application FR 2 388 391 an optical signal is transmitted into the interior of the switching device in order to detect the position in an insulated switching device. That optical signal is reflected from the interior, starting from a separate position of the switching device. The reflection signal which is produced thereby is then received by a separate receiving sensor. A corresponding position indication is then produced independently of the reflection signal. If the light path is interrupted by a movable part of the switching device, a new signal is received from the receiving element. A respective positioning signal is assigned or produced in the evaluation device according to the received signal.
A similar technique is described in Published East German Patent Application DD 269 040 A1. There an optical transmitting signal is directed to a movable part of a switching device. A positioning signal for the switching device is produced by the respective received signals according to the received reflection level. In that reference as well as in Published French Patent Application FR 2 388 391, the received reflection signal is solely monitored for its level and is likewise compared with a predetermined level, in particular a barrier.